Sleepy Ash

Sleepy Ash (スリーピーアッシュ, Surīpī Asshu) or Sloth (怠惰, Taidai), and mostly referred as Kuro  (クロ) throughout the series, is the deuteragonist of Servamp. Kuro, named by his Eve, Mahiru Shirota, is the Servamp of Sloth. He is the oldest of the eight Servamps. When he is exposed to sunlight, he transforms into a black cat.

Appearance
If Kuro is not in his cat form, he has shoulder-length, blue hair with his front bangs reaching his eyes. His eye color is red and he has big, dark bags under them. They are always half-lidded and express a feeling of boredom. Just like any other vampire, he has pointed teeth.

Kuro mostly wears a blue jacket which is a tad darker than his hair color with the hood pulled over his head, the black fur looking close to the one of his cat form. He also has a patch on his left shoulder with the Roman numeral 1, probably because he is the oldest of the seven sins. He is wearing the bell Mahiru gave him as their contract symbol around his neck as sometimes seen in official illustrations, which is apart from that mostly hidden under his clothes. His blue jacket is often buttoned open, either a simple black or white shirt hiding under it. On both sides, Kuro has chest pockets. The hem of his jacket splits into many threads, starting short at the front but grow in length as they reach his back. His white pants are skin-tight and held up with a red belt, which is rarely seen. Kuro wears long, black boots that almost reach his knees.

Hundreds of years before, Kuro wears long black hooded jacket with with white pants and darkish grey coloured suit underneath and a long scarf that he let loose.

As a cat, Kuro has black fur and red eyes. Around his neck he is wearing Mahiru's bell as a collar with red leather. His tail splits at its end into four, close to the threads at the back of his jacket in his human form.

Personality
Being the Servamp of Sloth, Kuro spends his time sleeping, lazing around or playing video games. He feels no shame in running away to avoid any trouble and refuses to take decisions for he doesn't want anything to be his fault, and he doesn't want to disappoint anyone. Kuro is a 'shut in' pacifist vampire, and rarely drinks Mahiru's blood, most of the time he refuses and drinks only when he is about to fight. He prefers staying at home rather than going out and seems to dislike the changes of temperature, according to him vampires are delicate to this.

Despite his lazy and at times comical nature (comical due to his laziness and arguments with Mahiru), he is shown to have a dark side. This is shown whenever anyone try to bring up his past that involves him killing the creator of Servamps. The mere mention of his past was enough to make Kuro who usually is nonchalant to become aggressive. He views himself as a monster, a fact that he dislikes, which caused him to refuse finding out more about his own race as it'll prove further how much of a monster he and his siblings are. He also refuse to turn any humans into vampires to make them his subclass, saying that they probably didn't want to become vampires, and that vampires shouldn't even exist.

Mahiru's straightforwardness and sincerity started to influence Kuro, though he always hides it by feigning uninterested and lazy as always. After Mahiru confronted him in his mind regarding his past action and assured him he is not alone, Kuro decides to stop running away and face his past, since then becoming more willing to fight and determines to stop Tsubaki.

He also prides himself in his cat form, often referring himself as a cute pet. He always uses his cuteness to attract the girls in Mahiru's class to give him foods, and sometimes also tries to use it to calm Mahiru when he thinks he is worrying too much, which unfortunately doesn't work for Mahiru since he already knows Kuro's characters all too well.

History
Kuro is the first and oldest of the seven servamps. At one point in the past, he was approached by with the decision to kill a certain person, the creator of the servamps by the C3. He called his remaining siblings to a family meeting to discuss whether they should accept the request or not. The discussion became an argument so they decided to do a majority vote, with Kuro making the final decision. Believing that the experiment that their creator was doing was too dangerous and to prevent another "monsters" like them to be born, Kuro decided that they should kill their creator and he willingly volunteered to be the one to do it. This decision caused him to have a falling out with Lawless, straining their relationship for years. As per request, Kuro went to Japan to do the job. Upon meeting his creator for the first time after hundreds of years, Kuro was surprised at the fact that the information was true, having a hard time believing that his creator is still alive. Kuro's resolve started to waver, but then convinced himself that his creator needs to be killed because his research is too dangerous, which he does. After killing his creator, however, Kuro began questioning whether he did the right thing or not, and this uncertainty haunted him since then.

Contract with Mahiru
Kuro first met Mahiru when the latter found him lying helplessly on street and decided to take him in as a pet. Soon, Kuro revealed himself as a vampire to Mahiru, and since he has given him a bell and a name, he has formed a temporary contract. To annul the contract, Kuro must not drink Mahiru's blood until 24 hours passed. Without any choice, Kuro sticks with Mahiru, going shopping with his friends despite his protest that he can't deal with sunlight, to which Mahiru retorts that it's already noon so he should be okay. On their way back, they were suddenly attacked by a vampire named Belkia who is targeting Kuro. Kuro kicks Belkia away before trying to run away, earning him a scold from Mahiru who tells him to help. Kurt simply replies that he can't stand against Belkia and he is one of people who thinks that someone else will deal with it. However, Kuro immediately changed his mind after watching Mahiru trying his best to save his friends, leading him to protect Mahiru. Kuro fought Belkia and powered up by drinking Mahiru's blood, finalizing the contract between him and Mahiru, making him a servamp. He easily defeated Belkia and intended to kill him, but Mahiru stopped him by reminding him of his own words that whatever happens onward, he (Mahiru) will be the one who make the decision and take the responsibility for it. Relenting, Kuro spared Belkia who was then picked up by another vampire the next day, Tsubaki.

First Encounter with Tsubaki
Tsubaki introduced himself as Kuro's youngest brother and the eighth servamp, the servamp of melancholy. However, Kuro doesn't recognise him as he never met him before and avoids fighting him, opting to run away. Tsubaki proceeds to attack Kuro, and despite the injuries, Kuro refuses to drink Mahiru's blood because he is too tired to fight back after using his strength against Belkia yesterday. They are saved by Servamp of Lust's interference, allowing them to escape.

Alliance with Misono and Lily
The next day, Kuro and Mahiru are taken by Misono Alicein, the Eve of Servamp of Lust that saved them before, Snow Lily. They demands Mahiru to give Kuro to them to fight against Tsubaki. While Mahiru objects since Misono and Lily are using force, Kuro quickly surrenders, forcing them to run away. After Mahiru and Kuro protected two of Lily's subclasses, they forms alliance with Misono and Lily. Mahiru and Misono gets into a quick argument regarding their respective servamps, which Kuro unsuccessfully tries to stop by using his cuteness. Despite this, both Mahiru and Misono quickly bonds due to Mahiru's friendliness, and when Mahiru asks Kuro how normal and important making friends is, Kuro simply says that he will only kill people who Mahiru tell him to kill and protect people who Mahiru tell him to protect, making Mahiru comments that Kuro has no independency.

Servamp Family Gathering
Shortly after forming alliance with Lily and Misono, the Lily decides to do a family meeting with the other servamps, giving Kuro and Mahiru the website address of vampire SNS where the subclasses of servamps are telling their troubles regarding Tsubaki's action. As he has said, Lily puts the location and time where the servamps are going to have a meeting, which is at a nearby family restaurant. Kuro tries to excuse himself so he doesn't need to go, but Mahiru forces him to go anyway. At the promised place, Kuro is confronted by Servamp of Gluttony, World End, who angrily asks him where he had been hiding for the last hundreds of years and demands to treat him all of the foods, which Kuro passively ignored. During the meeting, the servamps decided for Mahiru to be the leader and responsible of gathering the servamps. Lily then informs Mahiru that Kuro can give him a weapon to fight, much to Kuro's annoyance who wonders if Lily purposely holding a meeting so he can reveal that to Mahiru. When prompted by Mahiru, Kuro asks what does he need a weapon for. When Mahiru answers he wants it to protect himself and his friends, Kuro tells him to close his eyes as he materialize his weapon which is called "Lead", that takes a form of a broom. Kuro reminds Mahiru that when they first met, Mahiru attacked him with a mop and asks does he think cleaning tool equals a weapon, something that Mahiru denies.

Battle Against Sakuya and Belkia
Mahiru and Kuro are lured by Mahiru's close friend, Sakuya, who is revealed to be Tsubaki's subclass. Kuro and Mahiru are bound by another of Tsubaki's subclass, Otogiri's string, but Kuro able to free himself to shield Mahiru from Sakuya's attack before being stabbed down by Belkia's swords. When Mahiru calls out to him to drink his blood, Kuro tells Mahiru that it's useless for him to drink his blood now. He explains that servamps receives strength and motivation by drinking their eve's resolve flowing in their blood. Since Mahiru is unsure right now, even if he drinks his blood, it won't be enough to defeat both Belkia and Sakuya. When Mahiru decides to fight Sakuya after the latter injured Misono who came to help them, Kuro stops and tells Mahiru to retreat before he do something that he will regret, sensing that Mahiru is unsure of himself which unnerved him. As Mahiru fought Sakuya, Mahiru's doubt and fear overflowed within Kuro, causing him to lose control of his power and engulfs Mahiru. Before he can completely absorb Mahiru, Kuro is stopped by Servamp of Envy, Jeje, changing back into his cat form. The next day, Kuro asks the depressed Mahiru whether he is going to school or not and offers to play game together to get him to respond, but was taken aback when Mahiru instead asks about his injuries. Kuro then asks does he regret picking him up, when Mahiru tells him to shut up, Kuro is convinced that Mahiru is regretting it. Mahiru then takes him to eat at sushi bar where his uncle is working and meets Tsubaki by a chance. After Tsubaki tells Sakuya's story, he senses Kuro's murderous intent, who is hiding inside Mahiru's bag, prompting Tsubaki to leave. At the day of school festival, Kuro is thrown by Mahiru to stop Sakuya who was visiting the school, and after talking with Sakuya, Mahiru tells Kuro that he wants to stop Tsubaki so they need to become stronger together, making Kuro wondering whether they can face Tsubaki or not though he doesn't object Mahiru's decision.

Training
A month has passed, Mahiru still tries to train using his Lead properly while Kuro was playing a game. Mahiru demands Kuro to drink his blood so they can train together, but Kuro refuses. Mohair then apologizes for losing control of his power and want to become stronger. Kuro replies that they don't have time for that and he can't handle the responsibility that comes with it. Mahiru then realises that Kuro never wants to drink his blood, only drinking it when fighting and instead eat normal human foods. Mahiru tells Kuro to tell him if he ever want to drink his blood, but Kuro simply replies that he doesn't want to drink it. Kuro then opens the vampire SNS, only to find it has been shut down. On their way back, they are chased by a vampire, but it turns out that the vampire is actually running away from Mikuni and Jeje who are chasing after him and then kills him. Mahiru immediately bends on his knees, asking Mikuni to teach him to fight, prompting Kuro to tell him to lift his head, which Mahiru refuse. Mikuni then introduces himself as Misono's older brother, shocking Kuro and Mahiru. They continue their conversation at a restaurant where Mikuni reveals that Kuro is not only the oldest, but also the strongest servamp, much to Mahiru's doubt and Kuro states that he is only a cat. Mikuni then shifts the subject about the vampire SNS, having contacted the ones managing it and it turns out the website belonged to an institution. Hearing this, Kuro becomes uneasy and drops his drink, surprising Mahiru. Not wanting to hear more, Kuro goes outside, excusing himself by saying he will smoke. Mikuni states that as one of the highest rank vampire, Kuro must have bad experience with the institution. Outside, he is approached by a researcher belongs to the institution who asks for his cooperation, which Kuro coldly turns down, so the researcher left the letter to him. Lily then appears besides Kuro, commenting it reminds them of their old days. Kuro questions Lily's presence alone, to which Lily answers that he is called by Mikuni. When he returns inside with Lily, he returns just as Mahiru says to Mikuni that he will become stronger and he and Kuro will become real partners, surprising Kuro. Mikuni, Lily, and Jeje then agrees to help Mahiru becoming stronger, much to Mahiru's happiness. Seeing this, Kuro decides to hide letter from Mahiru.

Meeting Tetsu and Old Child
At school, Mahiru and Kuro overhears some people were talking about Kuro whom they referred with his street name, something that only known by people involves in vampire business. When Mahiru tries to catch up the person, he bumps into his senior Shuhei Tsuyuki who appoints Mahiru to help in summer festival holds by their school town. After school, while Mahiru helps with the festival, Kuro quickly enjoying himself by buying lots of foods from the stalls. While waiting for the fireworks, Mahiru laments how he thought that Shuhei is a vampire but turns out he was wrong, prompting Kuro to comment that being suspicious of people is not like him at all and he is fine with the way he is normally. However, Kuro quickly retracts his words, since Mahiru being suspicious of people will prevent him from doing reckless things. They are approached by a man who asks Mahiru to take the silver case he found to lost and found stall. Mahiru decides to take the silver case to the stall as Kuro warns him that they mustn't get too far away separated. Not long afterwards, explosions occurred, which originated from the similar silver case that Mahiru was carrying, so Mahiru quickly calls out for Kuro, who drinks his blood and jumps to the sky, throwing the silver case so it will explode without causing any casualties, but Kuro threw it too fast. Kuro assures Mahiru it will be okay since it will usually being blown by wind, but unfortunately, it fell straight down. Before Kuro could catch and throw it again, Tetsu Sendagaya, a person who Mahiru meets a few minutes ago at the festival, caught the bomb into his coffin where it exploded inside without destroying the coffin. Tetsu reveals himself to be the Eve of Servamp of Pride, Old Child, who now goes by the name Hugh. At Mahiru's apartment, the four of them continues their conversation where and Tetsu and Hugh agrees to accompany Mahiru and Kuro on their training with Mikuni, making Kuro comments that it's a pain because they're getting friendly with each other that most likely due to both Mahiru and Tetsu are plain. Meeting Mikuni to train, Kuro decides to play his game, leaving Mahiru and Tetsu to train alone. When Mahiru is questioned regarding knowledge about vampires and humans by Mikuni and Hugh, Mahiru answers that he prefers to hear about if from Kuro himself since he is his partner, surprising Kuro who then replies that it's too much to handle. The training ends once Tetsu uses his full power to remove all of Jeje's paper bags, the impact of the attack was enough to nearly blow away Kuro and Mahiru. Tetsu's strength makes Kuro feels that he is not needed in the training, making him glad. The next night, the training was cancelled due to one-sided hostility between Misono and Mikuni, so Kuro and the others decides to go to a family restaurant to discuss about their next move, though they are side tracked by the restaurant menu for a moment. When Mahiru suggests they ask the neutral organization, C3, for help, Hugh and Lily are against it due to what happened in the past when they received request from C3. Kuro quickly ends the conversation by saying that's not important right now. Kuro's interruption surprised Mahiru, but decides not to press the question further and they end the topic. Hugh and Lily then reveals that for the three days ago, Tsubaki had bombed 13 places related to C3, one of them was Mahiru's school. The news urged Mahiru and Kuro to go see the school that has been destroyed, which greatly shocked them before they are knocked unconscious by two C3 members.

Captured by C3
When he came to, Kuro finds himself at C3 base, accompanied by two of its researchers who demands for Kuro's cooperation. Kuro questions where Mahiru is. The researcher tells him that Mahiru is in another room and if he agree to help C3, they will release his eve. When the building was shaking, Kuro realises that Mahiru has escaped by himself, so refuse to cooperate and tells them to never force Mahiru into anything annoying again. Kuro lands right below where Mahiru has escaped. He quickly tells him that they're leaving, but Mahiru says there's something that picks his curiosity. Kuro says he is not curious, so he'll be taking his leave, forcing Mahiru to drag him to listen and they need to find the exit anyway. Finding a map, the map doesn't show a way out, distressing Mahiru. Mohair then asks Kuro about the abnormality that he experiences when they were separated. Kuro explains that if servamp and eve for separated beyond the distance limit for six hours, the eve will experience such as numb limbs, headaches and many more, and if eighteen hours passes both of them will become a cat, and finally if twenty four hours passes, the eve will die. Mahiru asks is there anything else he hasn't told him. Kuro tells him that there are many things he hasn't and probably will never tell him because Mahiru will stick more into vampire business which is annoying. Trusting Kuro, Mahiru respects Kuro's wish not to ask him and tells him not to forget that they are partners so if he is in trouble he will help him. While he is happy with Mahiru's understanding, Kuro decides to play it off by turning into cat and says it's annoying. Mahiru then explains that Tsubaki used to be in C3 and they may find out more about Tsubaki if they search through the reference room, an information that disturbs Kuro. The two decides to separate: Kuro looks for the exit while Mahiru looks for the reference room. Kuro tells Mahiru to yell if something happen so he can get away, annoying Mahiru who retorts he should be saving him and also yell if something happen. Kuro's inner self then points out Kuro's happiness after hearing what Mahiru told him and his nervousness if Mahiru finds out what happened in the past and the possibility that Mahiru will still trust him even if he knows what happened. He continues to points out how Kuro's actions and words are contradictory and suggests they break down C3 while they are inside the base since both of them hate it, at though which made Kuro feels uneasy. Hearing a gunshot, Kuro intimidates Shuhei Tsuyuki from behind before turning into his cat form to pick Mahiru. Shuhei tells Mahiru how much of a monster vampire is and they cannot be trusted, but Mahiru simply tells him the good side of vampires he has seen and to him they are his comrades that can protect people. While Mahiru thinks it's a simple thinking, Kuro comments it's more like Mahiru bulldozing rather than being simple, and he hate it with all his might, leading to another childish argument between the two. Shuhei decides to let the two of them go since they can't convince the Sloth Pair. When they got out, Kuro and Mahiru realises they are in front of the elevator at nearby station.

Djinn Rampage
Mahiru's classmate, Suzuhara, comes to Mahiru's apartment to return his cell phone, but it turns out she is possessed by a Djinn, an underclass creature that glue itself to humans and lead them to any nearby vampire to give the human to eat. In this case, the Djinn leads Suzuhara to Kuro for eat. Since Kuro doesn't want to drink blood, Mahiru exterminates the Djinn with his Lead. However, there are still more Djinns waiting in front of apartment, which Mahiru quickly exterminates before there are more victims. The extermination exhausts Mahiru who is carried by Kuro on their way to meet Tetsu and Hugh. Kuro explains that the mist around the town are also Djinns and cannot be seen by normal people. Tetsu and Hugh who were looking for the Sloth pair meets them by a chance and Hugh reveals that since yesterday the amount of Djinns appearing are unusually high and Djinn can only be killed by the Lead of an Eve, so there's nothing that Kuro and Hugh can do. They re confronted by Belkia who is about to drink a blood of woman possessed by a Djinn. Before he can do so, Kuro saves the woman by cutting off Belkia's arm, but Belkia reveals his hand is still intact. He then reveals their plan to unleash huge amount of Djinn from servamps and about to attack Kuro, but he suddenly vanished. Due the direness of the situation, Mahiru decides it's the time to gather all seven servamps.

Ambush on Alicein Mansion
Kuro and Mahiru are invited by Tetsu who allows one of rooms at his family hot spring hotel to be used for their gathering. Mahiru drags Kuro to do a patrol with Tetsu and meets Yuri, one of Lily's subclasses who asks for their help to save Misono because he is in trouble. At Misono's house, they are not allowed to meet Misono until Tetsu threatens them as suggested by one of the servants, Dodo. Finally allowed inside, the three are welcomed by the head servant, Yamane. Kuro becomes playmate to Lily's subclasses who feeds him lots of sweet until Misono's father, Mikado Alicein, approaches them and starts to show the pictures of Misono when he was a child. Mikado won't allow them to meet Misono out of fear of his son's safety, and when Mahiru refuses, they decides to use force. Yamane attacks Kuro and pins him to the wall while the vampire is in its cat form, but after a bit struggle, they're able to meet Misono who tells them to give him some time to talk with his father.

Three days later, worrying about Misono who hasn't contacted them since, Kuro, Mahiru, Tetsu, and Hugh goes back to the Alicein house but then finds the house overflowed with Djinns. Tetsu throws Kuro and Mahiru to the house ahead of him, bumping into Otogiri who was ordered by Tsubaki and succeeded destroying Lily's contract item. Tsubaki tells them his plan to destroy all the contract items of his siblings to not only weaken them, but also to unleash huge amount of Djinns. Mohair states that he never give Kuro anything, but to Mahiru's dismay, Kuro reminds him by showing the bell that he gave to him when they first met. Kuro and Mahiru arrives at the place where Lily and Misono are, witnessing Lily absorbed Misono due to losing control of himself, horrifying them. Kuro assures Mahiru that Misono is still alive inside Lily. Knowing this, Mahiru prepares to attack, but Kuro stops him because the vampire is the one who supposed to attack and Mahiru can't do anything against him. Kuro quickly gives up when Lily's attack almost hit him, scaring him, but he prepares to attack again when Lily charges onto Mahiru who blocks the attack with his Lead as he calls for Misono to come out. After freeing Misono and Lily returns to normal, Kuro is forced to get lots of towels to help the subclasses who are suddenly went ill. After Lily awakes, Kuro asks for Lily's help to tend his subclasses as Mahiru warns him not to strip, but was surprised when Lily tells that stripping is not his thing and he even want to cover his body even more, which is unusual for Lily. Mahiru points this out, but Kuro reminds him that it's a common sense not to strip in front of people, something that Mahiru confirms but coming from Lily is just not normal. After finished helping the subclasses, Mahiru starts to think that he should give a stronger contract item for Kuro so it won't be easily broken, but when Tetsu tries to destroy Kuro's cat bell, it remains unscathed, much to Kuro and Mahiru's relief who thought it would be destroyed. Hugh reveals that as long as the trust between servamp and eve is strong, it won't be easily broken. Mahiru comments that as vampires, they ought to know about themselves, but Kuro reveals that they don't want to know because it's not fun at all to find proofs of how much of a monster they are. Mikado then thanks them as he reveals about Misono's past and shows how much he thinks Misono is still a child. Mohair questions when Mikado is going to stop treating him as a child, which lead Mikado to leave in hurry, prompting Kuro to comment that Mahiru knows how to meddle into other people's business.

Meeting Licht and Lawless
After the incident at Alicein mansion, Kuro and the others are gathering at KTV after Hugh's subclass informs them there's a suspicious person who is strong enough to severely injured a subclass. When Hugh's subclass informs of the person's location, Mahiru and Kuro follows him. The person gives Kuro a dangerous vibe, so Kuro suggests that they should not get involved before noticing a hedgehog inside a cage the person is carrying which Kuro recognised. Mahiru then asks does Kuro has any subclass. Kuro explains he doesn't have one because it's too troublesome since he can't tell if the human still wants to live or not. Hearing Kuro's opinion for the first time, Mahiru tells Kuro that he will always believe in him so he should put more some efforts to be more open up. Kurt looks troubled by this statement while saying that it should be Mahiru who work hard. The person they are tailing finally face them, already noticing they are following him. He then immobilises and attacks Kuro with his Lead. Kuro notices his wounds are healing very slowly and is about to be attacked again if Mahiru didn't save him. He drinks Mahiru's blood and ties his attacker with his jacket tails, but the person easily frees himself. The hedgehog then interferes, introducing himself as Servamp of Greed, Lawless, while the attacker is his Eve, Licht Jekylland Todoroki. Lawless quickly refuses to ally himself and Licht with Mahiru and Kuro, instead telling Mahiru that if Kuro just make a decision, it can end at once by using a majority vote like they had done before, something that upset Kuro. Lawless continues to mocks Kuro that the latter hasn't change in a bad way, causing hostilities between the two. Lawless then comments that Pride, Lust, and Envy are on Kuro's side, and he doesn't want to get stuck on their side. Kuro retorts that Wrath and Gluttony are also present at the previous family meeting, to which Lawless simply replies that the two servamps are not so smart but he is sure they haven't forgotten what happened. Back at the lodging, they sees Licht appearing on TV as a famous pianist overseas, so Mahiru decides to try meet Licht by going to his concert, be he doesn't have any ticket to enter. Light's manager, Kranz Rozen, helps them in by giving a ticket stub. On their way, they spotted Otogiri, prompting them to go to the concert hall to stop the fight before it's too late, only to find Lawless has killed all of Tsubaki's subclasses that were sent to kill him and Licht. Lawless then attacks Mahiru after being annoyed by the latter's insistence they should work together, and Kuro protects him before he could hit the wall. Lawless then starts to reveal their past when they received a request from C3 to kill a certain someone that they decided with a majority vote, and Kuro was the one who made the final decision. As Lawless is telling this, Kuro starts to unleash his blood thirst. Before Lawless could reveal Kuro's decision, Kuro snaps and fight occurs between the two. They are stopped by Licht who kicks Lawless and immobilized Kuro using Mahiru's Lead. When hearing Licht's piano play, Kuro starts to have vision of his past that makes him depressed and unresponsive for the rest of the day no matter how many times Mahiru calls for him, going as far as indirectly intimidating Mahiru when his eve tried to ask about his past.

Abilities
Transformation Servamp Bond Claws Speed and Flight Endurance Inner Power Jacket Tails
 * Kuro can change into a black cat and into his human form at will. He can also speak when he is in his cat form. But, when he is exposed to sunlight, he automatically reverts back to his cat form. It is later revealed that he can turn into a giant lion.
 * When he drinks Mahiru's blood, the chain connecting them is visible and he appears to become more powerful.
 * He can extend his nails into long, sharp black claws, easily able to cut and skewer people and other vampires.
 * He is shown to have incredible speed and can jump high very easily, also shown that he is able to fly -which is rather strange as he is a shut in vampire and doesn't move round much.
 * Since he is immortal, he can't die. But, he heals very quickly and he was still able to fight even when he was stabbed through with a sword and still stood protecting Mahiru when he was being slashed at back and forth by knives. He was also knocked out by being shot at in the back by Envy's barrel guns.
 * When his control of his power was gone, he was much more faster, powerful, and ruthless; also unaware of what he is doing. He was shown beating Belkia, one of Tsubaki's servants, mercilessly. He grabbed Berukia's hair and was about to bite off his neck to kill him, revealing a new set of long, sharp canines, and he would have too if Mahiru hadn't stopped him by pulling on the chain around his neck and Envy knocking him out with his gun. He even hurt Mahiru in the process; grabbing his face with his claws, leaving three thick scratch marks above his right eye, and roughly biting him down on his neck.
 * He can move and use the tails at the end of his jacket to fight.

Mahiru Shirota (Eve)
For hundreds of years Kuro didn't have an Eve until Mahiru picked him up thus making them partners. Kuro initially only sticking around Mahiru due the contract made between them, and whenever he does something, mostly it was because Mahiru forced him to do it. Both often get into argument due to their contradicting personalities. Slowly, however, Mahiru's determination and sincerity started to influence him. Despite continuously saying that it's troublesome or he can't face it, he always protects Mahiru. He was often baffled by Mahiru's straightforwardness and willingness to trust him that he usually hides by feigning lazy, while in reality he is actually happy. Even though not shown clearly, Kuro grow to care for Mahiru and doesn't want to lose his trust. Their bond improved further after Mahiru helped him confront his past mistake and for the first time he tells Mahiru directly they are partners.

Lawless
Out of all his siblings, Kuro had a bad relationship with Lawless. Their hostility for one another originated when Kuro decided to kill their creator, something that Lawless strongly opposed. Unable to accept Kuro's action, Lawless told him that he will never forgive him, which continues for years. Whenever they met, Lawless always mocks and satirised his past action, which enough to make Kuro who usually prefers to be quiet to attack Lawless without any hesitation and shows clearly his murderous intent. After Kuro decided to face his past mistake, Kuro also apologized to Lawless regarding the incident by thanking him for not forgiving him back then, which Lawless accepts. Since then, the two spent their times together more often and it's also revealed that both were quite in common, both often likes to annoy Mahiru with their antics in particular.

C3
Kuro is shown to have a strong hatred for C3, the neutral group, due to the request given to him to kill his creator. Any conversation regarding C3 always makes Kuro uneasy, even yelling at Mahiru when he suggested if they could get C3's help. Since the incident, he decides to avoid any involvement with C3. Later on, when Kuro and Mahiru were captured by C3, and were escaping, Kuro's inner demon that controls his power was taunting him by saying that C3 brings back bad memories and that they should trash something up since they both still really hate C3. After C3 saved him and the others from Tsubaki and watches over them since then, Kuro decides to temporarily work with C3 to make sure they won't do as they please.

Tsubaki
Tsubaki seems to bear one-sided hatred Kuro for not knowing him being his youngest brother like his other siblings, mercilessly attacking him during their first encounter. Tsubaki actually has been looking for Kuro ever since he saw his lion form after he killed their creator, but didn't know it was him until Kuro showed up with that form together with Mahiru to rescue Lawless. Kuro initially didn't pay much attention towards Tsubaki and didn't really accept him as his youngest brother since he never heard of him. This changed after Tsubaki destroyed Lawless' contract item and revealed that he had witnessed Kuro killing their creator, forcing Kuro to believe that Tsubaki is truly a servamp. Coming into conclusion that Tsubaki's goal is to get revenge on him and his other siblings due to what happened with their creator, Kuro feels responsible and determines to stop and properly speak with Tsubaki to understand him, not wanting to repeat the same mistake he once done.

Quotes

 * "Ahhh...Now you're happy. Silly cat...Mahiru made you feel good...Right? But C3 brings back bad memories. If Mahiru discovers the 'Incident'...Will he still trust you? Are you worried? Mahiru's still a rookie...Happy birthday! You contradict yourself. You keep it all inside. You poor, pathetic boy! While we're at C3...Wanna trash something? After all, we still really hate them! Am I right?" (Kuro's inner demon taunting Kuro.)
 * "What you call simple, I call nagging." (to Mahiru.)
 * "Cat abuser." (to Mahiru)
 * "Paranoia's not my thing...Unlike you. Why look for trouble?"  (to Mahiru)
 * "Look at me guys...My cuteness will calm you..." (to the arguing Misono and Mahiru)
 * "Are you ever sorry...you found me...?" (to Mahiru)
 * "The pain! Wish I could die...But I can't." (Kuro complaining after escaping Tsubaki)
 * "Well, that's that! You are my master." (to Mahiru after drinking his blood, completing the contract)
 * "You'll...be the death of me." (to Mahiru after being stabbed to protect Mahiru)
 * "You are such a pain..." (to Mahiru)
 * "Close that! I hate sunlight..." (to Mahiru)
 * "I'm just your friendly neighborhood vampire." (to Mahiru)
 * "Humans are soo cruel...Meanie!" (to Mahiru)
 * "But the sun will kill me! Okay, I'm immortal. But still! Meeow!" (to Mahiru)
 * "We mix like oil and water." (to Mahiru)
 * "Reeeowr! Shame on you! Sucking up your cute little pet!" (Kuro complaining after Mahiru used the vacuum on him)
 * "Vampires don't age...Plus, I have a baby face." (Kuro to Mahiru)
 * "She hit me with a broom..." (Kuro to Mahiru after taking out the trash)
 * "Owww! The agony! An apple juice might help! Or a cola..." (to Mahiru)
 * "You read too much manga." (to Mahiru)
 * "Yes mommy..." (Kuro teasing Mahiru)
 * "Me want ramen! Yumm..." (to Mahiru)
 * "I follow your sign. If cancer gets bad news, I wanna know. And protect myself!" (to Mahiru)
 * "You always give one hundred and ten percent...that's way too much. Sit down." (to Mahiru who kept helping everyone who needed it)
 * "And never force  him(Mahiru) to do that again." (Kuro threatening the C3 employees after Mahiru had to use a dangerous amount of power to break out, causing Mahiru harm in the process)
 * "Where's Mahiru?" (Kuro to the C3 employees, mad that he was apart from Mahiru, putting Mahiru in danger)
 * "Housewife." (Kuro teasing Mahiru)
 * "Aww...It's okay. I just say, 'He told me to do it.' Free will is overrated." (to one of Berukia about Mahiru)
 * "Mahiru...do you trust me?" (to Mahiru)
 * "I have...lots...of them. But...I...can't tell you. Some things you shouldn't know. Some things...could kill you." (to Mahiru after he asked if he had anymore secrets)

Trivia

 * "Kuro" (クロ) literally translates into "black", Mahiru named him so due to his black fur when he is in cat form.
 * His favorite food is instant ramen and potato chips (with bouillon flavor).
 * His favorite ice cream flavor is cookies and cream.
 * He dislikes the sound of the alarm clock and the vacuum cleaner.
 * His hobbies are playing video games and looking for a comfortable pillow.
 * His favorite color is black.
 * In official illustrations Kuro is often drawn in both his cat and human form.
 * His catch phrase is 「めんどくせー」 (mendokuse) which roughly translates into "what a pain".
 * He hates vanilla ice cream.
 * He claims to dislike drinking blood from Mahiru.
 * Kuro becomes happy whenever Mahiru calls them partners.
 * In his cat form, a lot of girls at Mahiru's school find him adorable and sometimes dress him up in girly outfits.
 * Whenever Kuro really has to drink Mahiru's blood, he mostly does it in his cat form and bites him on the arm or leg, never his neck. The only time he drink from his neck is when Kuro lost control during the fight against Sakuya.
 * Kuro rarely drinks blood, and when offered, he rejects the idea or makes an excuse, preferring to eat junk food instead; the reason is not yet known.
 * In Drama CD, Licht took a liking to Kuro when he first saw him in his cat form. This continues even after knowing he's actually a vampire, most likely because Kuro is quiet as oppose to Hyde.
 * He has a patch on his left shoulder with the Roman numeral 1, probably because he is the oldest of the seven deadly sins; Snow Lily also has a patch on his left shoulder with the Roman numeral 7, and on the fifth volume cover Lawless had a patch with the numeral for 5.
 * In the first popularity poll he came first with 7145 votes.